The present invention relates to an electrodeionization apparatus and, more particularly to an electrodeionization apparatus which provides extremely high resistivity and low concentration of weak electrolytic anion of treated water, thereby continuously producing pure water with high purity.
An electrodeionization apparatus has a structure in which a plurality of cation-exchange membranes and a plurality of anion-exchange membranes are alternately arranged between electrodes in such a manner as to alternately form desalting compartments and concentrating compartments and the desalting compartments are filled with an ion exchanger. Voltage is applied between the cathode and the anode of the electrodeionization apparatus, water to be treated is introduced into the desalting compartments and concentrated water is introduced into the concentrating compartments, so that impurity ions permeate the membrane from the water to be treated to the concentrated water, thereby producing deionized water.
FIG. 12 is an exploded view showing the structure of the electrodeionization apparatus.
The electrodeionization apparatus includes a cathode end plate 1, a cathode 2 extending along the end plate 1, a cathode spacer 3 extending along the outer periphery of the cathode 2 which are superposed in this order. Further, a cation-exchange membrane 4, a frame 5 for defining a desalting compartment, an anion-exchange membrane 6, and a frame 7 for defining a concentrating compartment are superposed on the cathode spacer 3 in this order. The cation-exchange membrane 4, the frame 5 for defining a desalting compartment, the anion-exchange membrane 6, the frame 7 for defining a concentrating compartment compose one unit. The apparatus is composed of a plurality of such units superposed together. That is, membranes 4, frames 5, membranes 6, and frames 7 are repeatedly superposed one unit over the other unit. An anode 9 is superposed between the last anion-exchange membrane 6 and an anode spacer 8. An anode end plate 10 is superposed on the anodic electrode 9. The apparatus is tightened by bolts or the like.
The space defined by the inner surface of the frame 5 is the desalting compartment in which an ion exchanger 5R such as ion-exchange resin is filled. The space defined by the inner surface of the frame 7 is the concentrating compartment in which a spacer including a mesh spacer is disposed.
A direct electric current is supplied to pass between the anode 9 and the cathode 2, raw water to be treated is fed to the desalting compartment through a raw water inlet line 11, and concentrated water is fed to the concentrating compartment 8 through a concentrated water inlet line 12. The raw water fed to the desalting compartment flows through a layer filled with the ion-exchange resin whereby impurity ion in the raw water is removed so as to make the raw water deionized water which flows out through a deionized water outlet line 13.
Concentrated water fed to the concentrating compartment receives impurity ions permeating through the membranes 4, 6, and the concentrated water flows out through a concentrated water outlet line 14. Electrode water is passed within electrode compartments through introducing lines 15, 16 and discharging lines 17, 18, respectively.
An electrodeionization apparatus in which a desalting compartment is provided with vertical partition ribs for dividing the desalting compartment into cells being long in the vertical direction is disclosed in JP4-72567B. According to this electrodeionization apparatus having the desalting compartment divided into long cells by ribs in which ion-exchange resins are filled respectively, the channelizing phenomenon where the flow of water from the inlet to the outlet of the desalting compartment is partially one-sided is prevented and the compression and the ion-exchange resins in the desalting compartment is prevented from being compressed or moved.
In the electrodeionization apparatus of JP4-72567B, the number of the cells is limited because the cells are formed by dividing the desalting compartment in the vertical direction. That is a large number of cells can not be formed in the apparatus. Further, the flow of the water in a lateral direction is blocked by the ribs, so that the contact efficiency between the water and the ion-exchange resins is poor. In addition, the ion-exchange resins are compressed at lower portions of the cells so that the cells have a vacancy at upper portions thereof, whereby the rate of filling the ion-exchange resins tends to be poor.
It is an object of the present invention to provide an electrodeionization apparatus which overcomes problems described above, which has high contact efficiency between water and ion exchanger, in which water is stirred, and which has high filling density of the ion exchanger.
It is another object of the present invention to provide an electrodeionization apparatus which allows electric current to pass with partially different current densities in one desalting compartment.
The electrodeionization apparatus of the present invention has desalting compartments, each of which is divided into a plurality of cells by a partition member, and an ion exchanger is filled in the respective cells. At least a part of the partition member facing the cell is inclined relative to a normal flow or vertical flow direction of the water in the desalting compartment. The inclined part of the partition member allows permeation of the water, but prevents the ion exchanger to pass therethrough. Therefore, at least a part of the water flowing into the desalting compartment should flow obliquely relative to the normal flow direction of water, so that the water is dispersed overall to the desalting compartment, thereby improving the contact efficiency between water and ion exchanger and improving the deionization property.
The water flows in the cells with being stirred by the inclined part of the member, so that a boundary layer of concentration along the surface of the membrane whereby a dispersion resistance of ions is lowered and the apparatus becomes possible to be operated with a high flow velocity.
In an aspect of the invention, the apparatus has a large number of cells arranged vertically and laterally. A plurality of cells are arranged along the membrane surface both in the normal flow direction of water and a direction perpendicular to the normal flow direction, thereby extremely improving the contact efficiency between water and ion exchanger. Since the height of each cell is low, the ion exchanger is scarcely compressed. A vacancy is not formed at an upper portion in the cell, and the cell is filled evenly with the ion exchanger.
The configuration of each cell seen by projecting it upon the surface of the membrane is preferably a hexagon or a quadrangle. In case of the hexagon, the cells are preferably arranged in such a manner that a pair of sides thereof extend in the normal flow direction of water. In the case of a quadrangle, the cells are preferably arranged in such a manner that the respective sides thereof extend obliquely relative to the normal flow direction of water.
According to the present invention, all of the cells may be filled with the same ion exchanger, or instead thereof some of the cells may be filled with ion exchanger different from the ion exchanger filled in the other cells. For example, an anion exchanger may be filled in first cells, a cation exchanger may be filled in second cells, and an amphoteric ion exchanger (or a mixture of the anion exchanger and the cation exchanger) may be filled in third cells.
According to the present invention, each cell may be filled with an ion exchanger having one ion exchange characteristics or having plural ion exchange characteristics. For instance, a mixture of an anion exchanger and an amphoteric ion exchanger may be filled in the cell. A mixture of a cation exchanger and an amphoteric ion exchanger may be filled in the cell.
According to the present invention, the electrode may be composed of a plurality of small electrodes, insulated from each other, arranged corresponding to the first cells and the second cells in order to apply voltage, different from the voltage applied to the second cells, to the first cells filled with ion exchanger of the same ion exchange characteristics. The electrode may be composed of a plurality of small electrodes, insulated from each other, arranged corresponding to the first cells, the second cells, and the third cells in order to apply different voltage to the first cells, the second cells, and the third cells.
According to the present invention, the electrode may be composed of a plurality of small electrodes, insulated from each other, arranged corresponding to the arrangement of the cells.